1. Field of the Invention
The present invention relates generally to mold clamping apparatus of an injection molding machine which includes a driving device having a ball-screw driven by an electric motor by which a movable platen is reciprocally moved toward and away from a stationary platen, whereby a mold is accordingly closed and opened. More particularly, the present invention is concerned with a mold clamping apparatus having a novel structure wherein a hydraulic cylinder-piston mechanism is utilized to obtain an increased mold clamping force, and an effective method for controlling operation of the mold clamping apparatus.
2. Description of the Related Art
As a device for clamping a mold used for an injection molding machine, for example, there are known a direct-pressure type mold clamping device having a hydraulic cylinder-piston mechanism which generate a driving force directly applied to a movable platen so as to move the movable platen toward and away from a stationary platen for opening and closing the mold defined therebetween and so as to force the movable platen to the stationary platen for clamping the mold therebetween, and a toggle-type clamping device having a link mechanism in which the driving force is applied to the movable platen via the link mechanism. Another type of mold clamping device is also known, that device includes a ball-screw and an electric motor. In this ball-screw type clamping device, a rotational driving force of the electric motor is converted into a reciprocal driving force by the ball-screw, thereby executing the above-indicated mold opening and closing and clamping action, by utilizing this reciprocal driving force.
In the mold opening and closing actions, such a mold clamping device as described above is required to move the movable platen at a relatively-high velocity, in order to shorten a cycle time of a forming operation of the injection molding machine. In the mold clamping action, on the other hand, the mold clamping device is required to apply a relatively large driving force to the movable platen so that the movable platen is forced toward the stationary platen with a sufficiently large mold clamping force, thereby assuring a high accuracy of the injection molding. However, the conventional mold clamping device using the ball-screw suffers from difficulty in meeting both of these requirements.
The present inventor has been proposed in JP-U-3-3389 (publication number 3-3389 of Japanese Utility model application) a mold clamping device having an electric motor and a ball-screw, as well as a hydraulic cylinder-piston mechanism. This mold clamping device further includes an accumulator for accumulating a pressurized fluid, and is arranged such that the movable platen is moved by using the ball-screw for opening and closing the mold and is forced toward the stationary plate for clamping the mold therebetween by means of the hydraulic cylinder-piston mechanism and by utilizing the pressurized fluid accumulated in the accumulator during opening and closing the mold by using the ball-screw. This mold clamping device makes it possible to meet both of the above-indicated requirements. Namely, the proposed mold clamping device permits the mold opening and closing operation at a relatively-high velocity by using a combination of the electric motor and a small-sized ball-screw, and assures the generation of the relatively large mold clamping force with ease by utilizing the hydraulic cylinder-piston mechanism.
However, the proposed mold clamping device utilizes the pressurized fluid previously accumulated in the accumulator and then applied to a cylinder chamber of the cylinder-piston mechanism via a suitable switch valve. This requires the switching operation of the switch valve under a given hydraulic pressure generated by the pressurized fluid, needing a relatively large-sized switch valve and a relatively-large driving force for driving the large-sized switch valve, resulting in a time-consumed switching operation of the switch valve. In addition, the proposed mold clamping device suffers from a problem of pressure losses of the pressurized fluid during accumulated in the accumulator. Therefore, the proposed mold clamping device possibly suffers from insufficiency of the required characteristics.
It is therefore a first object of the present invention to provide an improved mold clamping apparatus which is capable of generating a desired driving force with ease by means of an electric motor and a ball-screw, for assuring a reciprocal movement of a movable platen at a relatively-high velocity, and generating a relatively-large mold clamping force with ease by using a hydraulic device.
It is a second object of the present invention to provide a suitable method for controlling an operation of such a mold clamping device.
The first object of the present invention may be achieved according to a first aspect of this invention, which provides a mold clamping apparatus of an injection-molding machine for clamping a mold consisting of a stationary mold half and a movable mold half, said mold clamping apparatus comprising: (a) a stationary platens fixedly disposed on a base of the injection-molding machine and being fixed with the stationary mold half; (b) a rear platen fixedly disposed on the base of the injection-molding machine and being opposite to and spaced apart from the stationary platen and; (c) a movable platen movably disposed between the stationary and rear platens and being fixed with the movable mold half; (d) an electrically-operated movable-platen-driving device of ball-screw type, including a first ball-screw shaft supported by one of the movable and rear platens, a first ball-nut threaded-engaged with the first ball-screw shaft and supported by the other of the movable and rear platens, and a movable-platen-driving-electric motor adapted to rotate the first ball-screw shaft and nut relative to each other so as to generate a relative longitudinal motion of the first ball-screw shaft and nut so that the movable platen is moved toward and away from the stationary platen to close and open the mold; (e) a pressure-generating cylinder device disposed on the rear platen and having a pressure-generating piston being moved by the relative longitudinal motion of the first ball-screw shaft and nut in order to generate a hydraulic pressure; (f) a mold clamping cylinder device disposed on the rear platen and adapted to generate a mold clamping force based on the hydraulic pressure generated in and applied from the pressure-generating cylinder device, the mold clamping cylinder device having a mold clamping ram which is connectable to the movable platen for applying the mold clamping force to the movable platen; and (g) an engaging device having a first operating position for connecting the mold clamping ram with the movable platen, and a second operating position for disconnecting the mold clamping ram from the movable platen, the mold clamping apparatus clamping the mold such that the movable platen is moved toward the stationary platen to close the mold therebetween, and the pressure-generating cylinder is operated to generate the hydraulic pressure, based on the relative longitudinal motion of the first ball-screw shaft and nut, while the engaging device is placed in the first operating position in order to apply the mold clamping force generated in the mold clamping cylinder device to the movable platen.
In the mold clamping apparatus constructed according to the first aspect of the present invention, the mold opening and closing operation is performed such that the ball-screw type movable-platen-driving device is used for reciprocally moving the movable platen between a mold opening position and a mold closing position of the movable platen. Namely, the first ball-screw shaft and the first ball-nut of the movable-platen-driving device are rotated relative to each other by the movable-platen-driving-electric motor of the movable-platen-driving device. This ball-screw mechanism is used to convert the relative rotation of the first ball-screw shaft and nut into the relative longitudinal motion or a relative displacement of the first ball-screw shaft and nut in the axial direction. The movable platen is directly moved by the longitudinal motion of the ball-screw shaft and nut in a direction toward and away from the stationary platen, for thereby opening and closing the mold. On the other hand, a mold clamping operation and a hydraulic pressure decreasing operation are performed by using the pressure-generating and the mold clamping cylinder devices, in addition to the movable-platen-driving device. Namely, the first ball-screw shaft and the ball-nut of the movable-platen-driving device are rotated relative to each other by the movable-platen-driving-electric motor, for converting the relative rotation of the ball-screw shaft and nut into the relative longitudinal motion of the ball-screw shaft and nut in the axial direction. The pressure-generating cylinder device is operated by the longitudinal motion of the first ball-screw shaft and nut for generating a hydraulic pressure therein. The hydraulic pressure generated in the pressure-generating cylinder device is applied to the mold clamping cylinder device so that the mold clamping cylinder device generates increased hydraulic pressure-generating the mold clamping force applied to the movable platen. Therefore, the movable platen is forced to stationary platen with the mold clamping force, resulting in clamping the mold between the movable and stationary platens.
In the thus constructed mold clamping apparatus, only the movable-platen-driving-electric motor is used as a power source, that is, generates a driving-force by its rotation. In the mold opening and closing action, the rotational driving-force of the electric motor is directly applied to the movable platen by means of the ball-screw device consisting of the ball-screw shaft and the ball-nut of the movable-platen-driving device. That is, the ball-screw device and the electric motor constitute a mechanical driving-force transmitting system for the mold opening and closing action. In the mold clamping action, on the other hand, the driving-force of the electric motor is transmitted to the movable platen, via a hydraulic device comprising the pressure-generating and the mold clamping cylinder devices. That is, the pressure-generating and mold clamping cylinder devices constitute a hydraulic driving-force transmitting system for the mold clamping action. In order to obtain a sufficiently large mold clamping force in the mold clamping action, the driving force of the electric motor is not directly applied to the movable platen by means of the ball-screw device, but is enlarged by and applied through the hydraulic device.
The mold clamping apparatus of the present invention constructed as described above does not require a large-sized or a high-power ball-screw device, even in the case where a relatively-large mold clamping force is required. Therefore, the mold clamping apparatus is capable of meeting the requirements for the rapid mold opening and closing action by means of the ball-screw device, and for assuring a sufficiently large mold clamping force by means of the small-sized ball-screw device.
In the mold clamping operation, the present mold clamping apparatus is operated such that the pressure-generating cylinder device is operated by the ball-screw device to generate the hydraulic pressure force. The hydraulic pressure force generated in the pressure-generating cylinder device is promptly delivered to the mold clamping cylinder device for thereby generating an increased hydraulic pressure force which is applied to the movable platen as the mold clamping force. Since the mold clamping force is generated by the thus constructed hydraulic device and directly applied to the movable platen, without being stored in a suitable accumulator, the mold clamping apparatus according to the first aspect of the present invention facilitates a control of the mold clamping force and is less likely to suffer from a problem of pressure loss of the working fluid in comparison with the conventional mold clamping apparatus using the above mentioned accumulator.
When the mold clamping apparatus changes its operation from the mold opening and closing operation to the mold clamping operation, and vice versa, a hydraulic circuit disposed between the pressure-generating cylinder device and the mold clamping cylinder device may be changed. In this case, the hydraulic circuit can be changed under a relatively low hydraulic pressure applied thereto, owing to the above-indicated elimination of the conventionally required accumulator, for example. This permits an easy and rapid changing of the hydraulic circuit. Thus, the mold clamping apparatus constructed according to the first aspect of the present invention assures a smooth shift from the mold opening and closing operation to the mold clamping operation.
In addition, the mold clamping apparatus constructed according to the first aspect of the present invention enjoys an advantage that the mold clamping force can be easily and precisely recognized by detecting hydraulic pressure forces in the pressure-generating and mold clamping cylinder devices with a suitable pressure sensor, for example.
It is noted that the pressure-generating and mold clamping cylinder devices may be either integrally formed with the rear platen, or alternatively independent of and fixed to the rear platen.
According to one preferred form of the first aspect of the present invention, the pressure-generating cylinder device further includes a biasing device adapted to bias a pressure-generating piston toward a fully retracted position thereof to increase a volume of a pressure-generating chamber of the pressure-generating cylinder device.
In this preferred form of the mold clamping apparatus, the provision of the biasing device permits an easy definition of an initial position of the pressure-generating piston, resulting in an easy and stable control of the operation of the pressure-generating cylinder device. In this respect, the biasing device is arranged to have a desired biasing force that is resistive to the driving force of the movable-platen-driving device that is applied to the biasing device during the mold closing action. The biasing device may function based on its suitably arranged biasing force to prevent a transmission of the driving force of the movable-platen-driving device to the pressure-generating cylinder device during the mold closing action, for prohibiting the operation of the pressure-generating cylinder device, and to allow the operation of the pressure-generating cylinder device, after the completion of the mold closing operation at which the driving force of the movable-platen-driving device, which is larger than the biasing force of the biasing device, is applied to the pressure-generating piston.
According to another preferred from of the first aspect of the present invention, the pressure-generating cylinder device further includes a lock device which is operable to fixedly connect the pressure-generating piston to a pressure-generating cylinder of the pressure-generating cylinder device, so as to prevent a movement of the pressure-generating piston relative to the pressure-generating cylinder.
In this preferred form of the mold clamping apparatus, the pressure-generating piston of the pressure-generating cylinder can be fixedly held in the predetermined initial position thereof, by means of the lock device, facilitating a control of the mold opening and closing positions of the movable-platen. Since the motion of the pressure-generating cylinder device can be stably prohibited by the lock device during the mold closing action, the mold closing operation can be stably operated by the movable-platen-driving device, without adverse influence of an unexpected operation of the pressure-generating piston during the rapid mold closing action. It should be noted that the lock device is releasable in the mold clamping action, so that the mold clamping apparatus can smoothly shifts its operation modes from the mold closing operation to the mold clamping operation.
According to a further preferred form of the first aspect of the present invention, the mold clamping device further includes a hydraulic device having a hydraulic circuit for fluid communication between a pressure-generating chamber of the pressure-generating cylinder device and a mold clamping chamber of the mold clamping cylinder device, and having a switch valve alternately connecting and disconnecting the pressure-generating chamber to and from the mold clamping chamber.
In this preferred form of the first aspect of the present invention, the mold clamping or mold closing operations of the mold clamping apparatus can be controlled by controlling the switching operation of the switch valve in order to allow and prohibit the fluid communication between the pressure-generating and mold clamping chambers. For instance, the switch valve is closed to prohibit the fluid communication between the pressure-generating and mold clamping chambers in the mold closing action for disabling the pressure-generating cylinder device, thereby stabilizing the mold closing action.
According to still further preferred form of the first aspect of the present invention, the pressure-generating piston is a hollow cylindrical member, and the pressure-generating chamber is partially defined by an outer circumferential surface of the hollow pressure-generating piston. The first ball-screw shaft is located in and extends through a bore of the hollow pressure-generating piston, and the first ball-nut is fixed to the hollow pressure-generating piston.
In this preferred form of the first aspect of the present invention, the pressure-generating piston is the hollow cylindrical member, making it possible to effectively arrange the first ball-screw shaft and nut by utilizing an interior space of the bore of the hollow cylindrical pressure-generating piston, leading to reduction in size of the mold clamping apparatus.
According to yet further preferred form of the first aspect of the present invention, the mold clamping cylinder device is disposed such that a center axis of the mold clamping cylinder device is aligned with a center axis of the movable platen, and the mold clamping ram comprises a hollow cylindrical member. The mold claming apparatus further comprising: a mechanical ram which is fixed at one of axially opposite ends thereof to the movable platen and partially located in a bore of the hollow mold clamping ram, the engaging device being operable to hold the hollow mold clamping ram in engagement with the mechanical ram.
In the above indicated preferred form of the first aspect of the present invention, the mold clamping force generated by the mold clamping cylinder device can be applied to a center portion of the movable platen, effectively preventing an undesirable attitude of the movable platen, even in the case where the only one mold clamping cylinder device is used. Thus, the mold clamping apparatus of this preferred form assures a stable attitude of the movable platen during the mold clamping operation.
In the above preferred form of the first aspect of the present invention may preferably be modified such the engaging device comprises a plurality of first engageable protrusions formed on an outer circumferential surface of the mechanical ram such that the first engageable protrusions extend in a circumferential direction of the mechanical ram and are spaced apart from each other at regular intervals in an axial direction of the mechanical ram, and an engaging member having a plurality of second engageable protrusions and supported by the mold clamping ram such that said engaging member is immovable in an axial direction of the mechanical ram and is movable toward and away from the outer circumferential surface of the mechanical ram, for engaging and disengaging said second engageable protrusions with and from said first engageable protrusions.
In this preferred form of the first aspect of the present invention, an engaging position of the second engageable protrusions relative to the first engageable protrusions can be optionally changed in the axial direction of the mechanical ram, namely in the direction of the reciprocal motion of the movable platen, so that the first and second engageable protrusions fully engaged with each other. This means that the mold clamping apparatus is applicable to various kinds of molds having different values of thickness, by only changing the engaging position of the first and second engageable protrusions in the axial direction taken into account the thickness of the employed mold.
In the above preferred form of the first aspect of the present invention may preferably comprises an positioning electric motor adapted to move the engaging member relative to the mechanical ram in the axial direction of the mechanical ram so that the second engageable protrusions of the engaging member is suitably positioned for an engagement with the first engageable protrusions of the mechanical ram.
This arrangement facilitates positioning of the first and second engageable protrusions relative to each other in the axial direction of the mechanical ram, in which direction the movable platen is reciprocally movable. Preferably, the positioning electric motor may be a servomotor, so that the first engageable protrusions and the second engageable protrusions are positioned relative to each other with high preciseness.
In the above preferred forms of the first aspect of the present invention may preferably be modified such that the mechanical ram comprises a hollow cylindrical member, and the mold clamping apparatus further comprises: an electrically-operated ejector device of ball-screw type having an ejector fixed to the movable platen, a second ball-screw shaft located in a bore of the hollow mechanical ram and fixed to one of the mechanical ram and the ejector, an second ball-nut threaded-engaged with the second ball-screw shaft and fixed to the other of the mechanical ram and the ejector; and an ejecting electric motor adapted to rotate the second ball-screw shaft and nut relative to each other so as to generate a relative longitudinal motion of the second ball-screw shaft and nut, thereby driving the ejector.
In the above-preferred form of the first aspect of the present invention, the ejector device is electrified. Further, the ejector device can be installed within the bore of the mechanical ram with improved spaced utilization, resulting in a small-sized electrically operated ejector device. Moreover the second ball-screw shaft and nut, which is adapted to apply the driving force to the ejector, can be disposed such that the center axis of the second ball-screw shaft is aligned with the center axis of the movable platen. This arrangement is effective to prevent undesirable inclination of the ejector due to an unbalanced application of the driving force to the ejector, for example, resulting in a stable attitude and operation of the ejector during the ejecting operation.
Preferably, the ejecting electric motor is fixedly disposed within the bore of the hollow mechanical ram, and the hollow mechanical ram has an air flow passage extending through the bore thereof.
In this arrangement, an interior space of the bore of the mechanical ram is efficiently utilized so that the ejecting electric motor is disposed within the bore of the mechanical ram. In this case, the electric motor may be elongated along the axial direction of the mechanical ram, resulting in an increase in power of the ejecting electric motor, without an increase in the size of the mold clamping apparatus. In addition, the air passage permits ventilation of the interior space of the bore of the mechanical ram, owing to the axially reciprocal movement of the mechanical ram, effectively eliminating a problem of heat generated by the ejector electric motor.
According to yet another preferred form of the first aspect of the present invention, the pressure-generating cylinder device comprises a plurality of pressure-generating cylinder devices disposed about a center axis.
In this preferred form of the first aspect of the present invention, the use of the plurality of pressure-generating cylinder devices effectively downsizes each of the pressure-generating cylinder devices, leading to reduction in size of the mold clamping apparatus.
This preferred form of the first aspect of the present invention may preferably be modified such that each of the plurality of pressure-generating cylinder devices comprises: the pressure-generating piston in the form of a hollow cylinder; the pressure-generating chamber partially defined by an outer circumferential surface of the hollow pressure-generating piston; the first ball-screw shaft located in and extending through a bore of the hollow pressure-generating piston; the first ball-nut fixed to the hollow pressure-generating piston; and the movable-platen-driving-electric motor being fixedly supported by the movable platen and being adapted to rotate the first ball-screw shaft and nut relative to each other.
In the above-preferred form of the first aspect of the present invention, the movable-platen-driving-electric motor is supported by the movable platen, effectively reducing the overall length of the mold clamping apparatus. Moreover, the plurality of the first ball-screw shafts and nuts are disposed about the center axis of the movable platen, assuring a stable application of the driving force to the movable platen via the plurality of the first ball-screw shaft, resulting in an improved stability of the mold opening and closing operation of the mold clamping apparatus.
According to still yet another preferred from of the present invention, the mechanical ram comprises a hollow mechanical ram and the first ball-screw shaft is located in a bore of the hollow mechanical ram.
This arrangement permits that the first ball-screw shaft of the movable-platen-driving device can be arranged within the bore of the mechanical ram with high space utilizing efficiency. In addition, the first ball-screw shaft can be arranged such that the axis of the first ball-screw shaft is aligned with the center axis of the movable platen. Thus, the driving force generated by the one movable-platen-driving-electric motor is stably applied to the movable platen via the first ball-screw shaft.
In the above-preferred form of the invention, preferably, the first ball-screw shaft is axially immovably supported by the base of the injection-molding machine, and the pressure-generating piston is slidably movable within the bore of the mechanical ram so as to constitute the pressure-generating cylinder device, while the first ball-nut is fixed to the pressure-generating piston.
In this preferred form of the invention, the first ball-nut is effectively disposed within the bore of the mechanical ram, with improved space utilization, effectively reducing the axial length of the mold clamping apparatus.
According to yet still another preferred form of the first aspect of the present invention, the mold clamping device further comprising: the first ball-screw shaft of the movable-platen-driving device supported by the base of the injection-molding machine such that the screw shaft is rotatable about an axis thereof and is immovable in an axial direction thereof; the movable-platen-driving-electric motor adapted to rotate the first ball-screw shaft in forward and reversed directions; a hollow mechanical ram radially outwardly disposed of the first ball-screw shaft and fixed at one of axially opposite ends thereof to the movable platen such that the hollow mechanical ram is movable in an axial direction thereof relative to the base of the injection-molding machine and is not rotatable about the axis thereof; the pressure-generating piston radially inwardly disposed of the mechanical ram such that the pressure-generating piston is reciprocally slidably movable in an axial direction of the mechanical ram and is not rotatable about an axis of the mechanical ram, the pressure-generating piston cooperating with the mechanical ram to define a pressure-generating chamber therebetween whose volume is decreased by a movement of the pressure-generating piston toward one of axially opposite ends of the mechanical ram, the pressure-generating piston and the pressure-generating chamber cooperating with each other to constitute the pressure-generating cylinder device; a biasing device adapted to bias the pressure-generating piston of the pressure-generating cylinder device relative to the mechanical ram such that the pressure-generating piston is biased toward one of axial ends of the pressure-generating cylinder device remote from the movable platen; the first ball-nut of the movable-platen-driving device, threaded engaged with the first ball-screw shaft and fixed to the pressure-generating piston of the pressure-generating cylinder device, the first ball-screw shaft and nut being rotated relative to each other so as to reciprocally move the pressure-generating piston; the mold clamping cylinder radially outwardly disposed of the mechanical ram and fixedly supported by the base of the injection-molding machine; the mold clamping ram of the mold clamping cylinder device radially outwardly disposed of the mechanical ram and radially inwardly of the mold clamping cylinder such that the mold clamping ram being slidably movable in an axial direction of the mold clamping cylinder, the mold clamping ram cooperating with the mold clamping cylinder to define therebetween a mold clamping chamber; a positioning electric motor adapted to move the mold clamping ram relative to the mold clamping cylinder for positioning the mold clamping ram relative to the mold clamping cylinder in the axial direction of the mold clamping cylinder; a hydraulic device having a hydraulic circuit for fluid communication between the pressure-generating chamber of the pressure-generating cylinder device and the mold clamping chamber of the mold clamping cylinder device, and having a switch valve alternately connecting and disconnecting the pressure-generating chamber to and from the mold clamping chamber, so that the hydraulic pressure generated in the pressure-generating chamber is transmitted to the mold clamping chamber so as to generate a hydraulic pressure in the mold clamping chamber and apply the hydraulic pressure to the mold claming ram of the mold clamping cylinder device as a hydraulic driving force, when the pressure-generating chamber and the mold clamping chamber are communicate with each other, and the hydraulic pressure generated in the pressure-generating chamber is not applied to the mold clamping chamber so as to move the piston of the pressure-generating cylinder device together with the mechanical ram by rotating the first screw-shaft, thereby opening and closing the mold, when the pressure-generating chamber and the mold clamping chamber are disconnected from each other; an engaging device disposed between the mold clamping ram of the mold clamping cylinder device and the mechanical ram, and being operable for engaging the mold clamping ram and the mechanical ram with each other in order to apply the hydraulic driving force of the mold clamping ram of the mold claming cylinder device to the mechanical ram as a mold clamping force.
In this preferred form of the first aspect of the present invention, the pressure-generating chamber in the form of a hollow cylindrical shape is effectively defined by the inner circumferential surface of the mechanical ram and the outer circumferential surface of the pressure-generating piston. This arrangement permits a formation of the hydraulic chamber with excellent space utilization, and effectively provides a space for disposing the biasing device, for example, between the mechanical ram and the pressure-generating piston.
According to yet, yet still another preferred from of the first aspect of the present invention, the mold clamping apparatus further comprising: a plurality of the pressure-generating cylinder devices including a plurality of pressure-generating cylinders fixed to the rear platen and disposed about an extension of a center axis of the movable platen so as to extend parallel to the center axis of the movable platen, a plurality of the pressure-generating pistons each having a hollow cylindrical shape, and being slidably movable within the plurality of pressure-generating cylinders, respectively, and a plurality of the pressure-generating chambers partially defined by outer circumferential surfaces of said hollow pressure-generating pistons, and having a volume which is decreased by a sliding movement of the plurality of the pressure-generating pistons in a direction remote from the movable platen; a plurality of the movable-platen-driving-electric motors disposed on the movable platen and adapted to rotate the first ball-screw shafts in forward and reversed direction; a plurality of the first ball-nuts thread-engaged with the plurality of the first ball-screw shaft and fixed to the plurality of pressure-generating pistons; a plurality of biasing devices adapted to bias the pressure-generating pistons of the pressure-generating cylinder devices toward the movable platen in an axial direction; the mold clamping cylinder device including the mold clamping cylinder fixedly disposed on the rear platen such that a center axis of the mold clamping cylinder is aligned with the center axis of the movable platen, the mold clamping ram having a hollow cylindrical shape being slidably movable within the mold clamping cylinder, and the mold clamping chamber partially defined by an outer circumferential surface of the mold claming ram and having a volume which is decreased by a sliding movement of the mold clamping ram in a direction remote from the movable platen; a hydraulic device being operable to prohibit a fluid communication between the pressure-generating chambers and the mold clamping chamber for fixedly positioning the pressure-generating pistons relative to the pressure-generating cylinders, so that the movable platen fixed with the pressure-generating cylinders is moved toward and away from the stationary platen for closing and opening the mold, while being operable to allow a fluid communication between the pressure-generating chambers and the mold clamping chamber for a slidably movement of the pressure-generating piston, so that hydraulic pressure generated in the pressure-generating chamber by the rotation of the first ball-screw shaft is applied to the mold clamping chamber of the mold clamping cylinder device, thereby applying a hydraulic driving force to the mold clamping ram; a mechanical ram fixedly disposed on the movable platen so as to extend toward the rear platen along the center axis of the movable platen; the engaging device disposed between the mechanical ram and the mold claming cylinder device, and being operable to engage the mechanical ram and the mold claming ram relative to each other for applying the hydraulic driving force generated by the mold clamping cylinder device to the mechanical ram as the mold clamping force; and an electrically-operated ejector device of ball-screw type including an ejector plate fixed to the movable plate, a second ball-screw shaft located in a bore of the hollow mechanical ram and fixed to one of the mechanical ram and the ejector, an second ball-nut threaded-engaged with the second ball-screw shaft and fixed to the other of said mechanical ram and the ejector; and an ejecting electric motor adapted to rotate the second ball-screw shaft and nut relative to each other so as to generate a relative longitudinal motion of the second ball-screw shaft and nut, thereby driving the ejector.
The second object of the present invention may be achieved according to a second aspect of this invention, which provides a method of controlling operation of a mold clamping apparatus constructed according to the first aspect of the invention, wherein the apparatus further includes a plurality of first engageable protrusions formed on one of the mold clamping ram and the movable platen such that the plurality of first engageable protrusions are spaced apart from each other at regular intervals in a direction in which the mold clamping ram and the movable platen are moved relative to each other, and an engaging member formed on the other of the mold clamping ram and the movable platen and having a plurality of second engageable protrusions which are engageable with the first engageable protrusions, the engaging member being moved toward and away from the first engageable protrusions, the method comprising the steps of: (a) fixing a sample mold consisting of a movable mold half and a stationary mold half to said movable and stationary platens, respectively, the sample mold having a thickness smaller than that of a employed mold to be fixed; (b) moving the movable platen to a mold closing position thereof where the stationary and movable mold halves are held in contact with each other to close the sample mold between the stationary and movable platens; (c) detecting an axial position of the movable platen which is placed in the mold closing position, as an initial position of the movable platen in the axial direction; (e) adjusting an axial position of the mold clamping ram relative to the mold clamping cylinder in order to assure an engagement of the first and second engageable protrusions; (f) detecting an adjusted axial position of the mold clamping ram as an reference position of the mold clamping ram in the axial direction; and (g) adjusting a position of the mold clamping ram relative to the mold clamping cylinder in the axial direction, based on detected data with respect to the initial position of the movable platen and the reference position of the mold clamping ram, in order to assure the engagement of the first and second engageable protrusions, when the movable platen is held in the mold closing position to close an optional mold interposed between the movable and stationary platens.
In a method of controlling the operation of the mold clamping apparatus according to the second aspect of the present invention, the mold clamping ram of the mold clamping cylinder device and the movable platen are stably engaged or connected with each other by means of the engaging device, immediately after the movable platen has been moved to the mold closing position by the rectilinear driving force of the movable-platen-driving device of ball-screw type, irrespective of the thickness of the optional mold. This arrangement permits effectively stabilizing injection-molding operation using the mold clamping apparatus, and effectively shortening a cycle time of the injection molding operation using the mold clamping apparatus.
The second object of the present invention may also be achieved according to a third aspect of this invention, which provides a method of controlling operation of a mold clamping apparatus constructed according to the first aspect of the invention, wherein the movable-platen-driving-electric motor comprises an electric servomotor. In this case, the method further comprising the steps of: controlling an output torque of the electric servomotor, based on a hydraulic pressure in the pressure-generating chamber of the pressure-generating cylinder device, during the mold clamping apparatus clamp the mold.
In the third aspect of the invention, the electric servomotor is employed as the movable-platen-driving-electric motor, assuring an improved accuracy of control for positioning the mold, or the movable platen. Therefore, the presently preferred method makes it possible to control with high preciseness the motion of the movable platen, when the mold clamping apparatus is operated for protecting the mold in response to a detection of a foreign member existing between the mold halves, for example. In the presently preferred form of the method, the position of the mold upon ejecting the molded article from the mold, can be suitably controlled with high preciseness, thereby reducing a ratio of fail in chucking of the molded article ejected from the mold. For instance, the output torque of the servomotor may be controlled based on the hydraulic pressure force in the mold clamping chamber which is applied as the mold clamping force to the movable platen, permitting a control of the mold clamping force with high-preciseness and with high responsibility.
Alternatively, the second object of the present invention may also be achieved according to a fourth aspect of this invention, which provides a method of controlling operation of a mold clamping apparatus constructed according to the first aspect of the invention, wherein movable-platen-driving-electric motor comprises an electric servomotor. In this case, the method further comprises the steps of: decreasing a hydraulic pressure in the mold clamping chamber by gradually decreasing a value of an output torque of the servomotor to a predetermined value so that a decrease of a hydraulic pressure in the mold clamping chamber is completed.
In the above form of the method, the output torque of the electric servomotor is controlled to be gradually reduced, effectively, stably and easily decreasing a magnitude of impact occurring upon decreasing the mold clamping force in a mold clamping force decreasing operation.
Further, the second object of the present invention may also be achieved according to a fifth aspect of this invention, which provides a method of controlling operation of a mold clamping apparatus constructed according to the first aspect of the invention, wherein the movable-platen-driving-electric motor comprises an electric servomotor. In this case, the method further comprising the steps of: decreasing a hydraulic pressure in the mold clamping chamber by changing gradually or continuously a rotation speed of the servomotor in a direction for generation a reduction of the hydraulic pressure in the mold clamping chamber, until is detected at least one of conditions: that a predetermined period of time has passed which is required for decreasing the pressure in the mold clamping chamber, and that the pressure in the mold clamping chamber has been reduced to a predetermined level.
In the above form of the method, the rotation speed of the servomotor is controlled, thereby effectively, stably and easily decreasing a magnitude of impact occurring upon decreasing the mold clamping force in the mold clamping force decreasing operation. In particular, since the servomotor is controlled based on its rotating velocity, the mold clamping force can be continuously reduced in the mold clamping force decreasing operation.
The above preferred forms of the method of the present invention, may be modified such that the mold clamping apparatus further includes a biasing device adapted to bias the pressure-generating piston toward a fully retracted position thereof to increase a volume of a pressure-generating chamber of the pressure-generating cylinder device. In this case, the method further comprises the steps of: controlling an output torque of the servomotor taken into account of a force required for moving the pressure-generating piston against the biasing force applied thereto.
In the above preferred form of the second aspect of the invention, the servomotor is controlled taken into account of biasing force of the biasing device, so that the presently preferred control method permits the high-precisely control of the mold clamping force, while assuring the biasing device to generate a predetermined biasing force.